This invention relates to a magnetic disk assembly and, more particularly, to such an assembly wherein the magnetic disk is provided with a hub member having a non-circular opening which functions to center the magnetic disk on a drive shaft. The invention also relates to a magnetic disk cartridge which contains the magnetic disk assembly and, additionally, to apparatus which uses the magnetic disk cartridge to record and/or reproduce signals on the magnetic disk.
Magnetic disk cartridges are known wherein a magnetic disk assembly is housed within a jacket which serves to protect the magnetic disk from crumpling, folding or other damage, particularly when the magnetic disk cartridge is not in use or when that cartridge is shipped. One type of magnetic disc which is housed within such a jacket is the so-called "floppy" disk or diskette. To permit a magnetic transducer to gain access to the disk and thus record or reproduce signals thereon, the jacket is provided with a window through which the transducer is inserted into magnetic contact with the surface of the magnetic disk. Also, the jacket is provided with a generally central aperture through which a disk drive shaft may be inserted into driving engagement with the center hub of the magnetic disk so as to rotate the disk when the shaft is driven.
In order to permit satisfactory rotation of the magnetic disk within the jacket, it may be desirable to provide sufficient play of the disk hub relative to to the drive shaft opening in the jacket. However, such play, which generally permits lateral movement of the magnetic disk within the jacket, may affect the proper positioning of the magnetic disk when the jacket is loaded into record/reproducing apparatus. More particularly, when such a jacket is loaded into record/reproducing apparatus, the aforementioned lateral movement of the magnetic disk due to the play of the disk hub relative to the jacket opening may result in mis-positioning of the disk such that the magnetic transducer is off-set from the desired relative position thereof on the disk. Hence, if a particular track has been recorded on the magnetic disk by a transducer during a previous recording operation, the play of the magnetic disk within the jacket may mis-position the transducer when the jacket subsequently is loaded into the same or different record/reproducing apparatus for a subsequent playback operation. This mis-position of the transducer may result in a mis-alignment thereof relative to the desired track.
Another difficulty which may arise due to the play of the magnetic disk relative the jacket is that when the jacket is loaded into record/reproducing apparatus, the center of the disk might not be coincident with the axis of the drive shaft that is inserted into the disk hub. Such non-coincidence may result in eccentric rotation of the disk by the shaft.
In order to provide proper centering of the magnetic disk housed within a jacket when the jacket is loaded into record/reproducing apparatus, it has been proposed to form the hub with a non-circular opening for receiving the drive shaft of the record/reproducing apparatus. One example of a magnetic disk assembly having a hub with a non-circular opening is described in U.S. Pat. No. 4,149,207. The non-circular opening described in this patent includes two straight edges which form an angle with each other on the order of about 60 degrees. When a drive shaft is inserted into the non-circular opening, both of these straight edges are brought into tangential contact with the drive shaft and thereby bring the center of the disk into coincidence with the axis of the shaft. However, the minimum diameter of this non-circular opening is greater than the diameter of the drive shaft. Hence, although the straight edges of this opening are in tangential contact with the drive shaft, the shaft is free to rotate within the opening without also rotating the hub and magnetic disk. Rather, to effect rotation of the disk, an additional pin on the drive mechanism is inserted into a separate aperture on the disk, and the pin is driven to rotate with the drive shaft, thereby exerting a rotary force on the aperture into which it is inserted and, thus, resulting in rotation of the disk. Thus, according to this patent, the angled straight edges of the non-circular opening in the disk serve to center the disk on the drive shaft, but a separate rotary pin is needed in order to rotatably drive the disk. The drive shaft is not capable of both centering the disk thereon as well as driving it.
The disk drive described in the aforementioned patent is not satisfactory for use with a magnetic disk having a relatively small diameter. For example, if the magnetic disk exhibits a diameter on the order of 50 mm, such a small dimension does not permit additional room on the disk for a separate aperture into which a drive pin may be inserted for rotating the disk. Rather, it is important that the drive shaft perform the functions of centering the disk thereon and rotatably driving it.